Heart and Muscle Metabolism in Barth Syndrome

Barth syndrome (BTHS) is an X-linked disorder characterized by abnormal cardiolipin metabolism, mitochondrial dysfunction, muscle wasting and heart failure. BTHS is a particularly significant disease as it is often fatal in childhood and there are no approved therapies for BTHS other than the standard treatment of heart failure. Therefore novel areas of research and platforms in which to test new therapies are highly needed. Through state-of-the-art and innovative methodologies, this project will focus on the novel role of skeletal muscle and heart nutrient (glucose, fatty acid, and amino acid) metabolism in the pathogenesis of BTHS. Phenotypic information regarding skeletal muscle and heart nutrient metabolism in BTHS and how it may relate to energy production and function of these organs is lacking and is significant as this may advance our understanding of the underlying pathogenesis of BTHS. With this understanding, safe and efficacious therapies can be targeted for BTHS. The investigators' overall hypothesis is that impaired fatty acid metabolism in skeletal muscle and the heart produces a fuel deficit in these organs leading to impaired energy production, exercise intolerance and heart failure. Further, as a consequence of impaired fatty acid metabolism in skeletal muscle and the heart, protein breakdown (wasting) in skeletal muscle and the heart occurs to provide amino acids as compensation for this inadequate fatty acid energy supply, thereby worsening heart and skeletal muscle function in BTHS. The investigators' aims to address this hypothesis in 30 young adults and children with BTHS and 30 healthy, age, puberty stage and activity level matched controls ages 8-35 years are:

• To characterize skeletal muscle and heart nutrient metabolism and 2) To examine the relationship between skeletal muscle and heart nutrient metabolism, energy production and function (exercise tolerance and heart function). As an exploratory aim, we will examine mechanistic molecular pathways of nutrient metabolism; specifically protein breakdown, mitochondrial function and fatty acid metabolism, in human myocytes derived from inducible pluripotent stem cells (from skin fibroblasts) obtained from adults and children with BTHS and from adult controls. Skeletal muscle nutrient metabolism will be quantified by stable-isotope tracer methodology and mass spectrometry, heart nutrient metabolism using radio-isotope tracer methodology and PET imaging, skeletal muscle and heart energy production using magnetic resonance spectroscopy, skeletal muscle function by graded exercise testing and indirect calorimetry, heart function by echocardiography, and myocyte nutrient pathway mechanism examination by pluripotent stem cell induction and protein and RNA expression analyses.

Inclusion criteria

• confirmed diagnosis of BTHS or healthy control
• age 8-35 years
• sedentary (physically active less than 2x/wk)
• stable on medications for ≥ 3 months including ß-blockers, ACE inhibitors, digoxin
• lives in North America, the UK, Europe, South Africa or other locations feasible for travel to the US

Exclusion criteria

• current unstable heart disease
• diabetes or other known concurrent disease that may affect nutrient metabolism